Title:

Hydraulic Stimulation of Well 27-15, Desert Peak Geothermal Field, Nevada, USA

Authors:

Ethan CHABORA, Ezra ZEMACH, Paul SPIELMAN, Peter DRAKOS, Stephen HICKMAN, Susan LUTZ, Katie BOYLE, Amber FALCONER, Ann ROBERTSON-TAIT, Nicholas DAVATZES, Peter ROSE, Ernie MAJER, Ste

Key Words:

EGS, Desert Peak, stimulation, hydrofrac

Geo Location:

Desert Peak, Nevada

Conference:

Stanford Geothermal Workshop

Year:

2012

Session:

Enhanced Geothermal Systems

Language:

English

Paper Number:

Chabora

File Size:

1926 K

View File:

Abstract:

Following an integrated study of fluid flow, fracturing, stress and rock mechanics, silicified rhyolite tuffs and metamorphosed mudstones were hydraulically and chemically stimulated in Desert Peak well 27-15 as part of an Enhanced Geothermal System (EGS) project. The target well is located on the margins of an operating geothermal field, and the stimulated zones lie at a depth from 3,000 to 3,500 feet where temperatures range from 355 to 385°F. A long initial period of shear stimulation was carried out at low fluid pressures (less than the least horizontal principal stress, Shmin), which increased injectivity by more than one order of magnitude. After this, chelating agents and mud acid treatments were used to dissolve mineral precipitates and open up partially sealed fractures. This chemical stimulation phase temporarily increased injectivity, but led to increased wellbore instability. After a wellbore clean-out, a large-volume hydraulic fracturing operation was carried out at high pressures (exceeding Shmin) and high injection rates over 23 days to promote fluid pressure transfer to greater distances from the borehole, resulting in an additional 4-fold increase in injectivity. Locations of microearthquakes (MEQs) and tracer testing demonstrate growth of the stimulated volume between well 27-15 and active geothermal wells located approximately 0.25 to 1.25 miles to the SSW. The seismic array has been augmented and a final phase of hydraulic fracturing and shear stimulation is being considered to further improve permeability in the region around well 27-15.


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